|Plant life exists in a complicated relationship with water—not only as an ingredient for life and photosynthesis, but, through interactions, for the soil and the climate as well. Is this relationship beneficial? Or should the World Bank reconsider reforestation projects in the interests of water conservation and climate change? In this presentation on October 12, 2006, at the World Bank’s headquarters in Washington, DC, Sampurno Bruijnzeel, Associate Professor of Eco-hydrology at Vrije University in Amsterdam, explained why trees contribute to steady flows of clean water, based on 30 years of experience with tropical hydrology. Kenneth Chomitz, Senior Advisor for the World Bank’s Independent Evaluation Group, chaired the meeting.
Bruijnzeel addressed the question of whether trees should be planted for ecological projects, and the environmental consequences of that decision. He began by setting the scene of increasing population, resulting soil degradation, and increasing climate anomalies. He asked whether forests actually increase rainfall and prevent natural disasters, and noted that most people tend to answer in the positive. Bruijnzeel then discussed the real interaction of forests (and deforestation) with rainfall, cloud development, and climate effects.
Bruijnzeel noted in more depth the effects of soil degradation on the watershed, and how plants affect water retention and droughts. He also raised the point of water yield, where trees remove water from the streamflow but help to regulate it during dry seasons. From this point he moved to the effects of replanting forests on water yield and soil retention. Audience members asked questions about completely depleted water tables, water quality after paved roads, and whether forests are always beneficial.